Nanooptics and photonics

Photochromic centers of Gd3Ga5O12:Co single crystals
D. Sugak 1,2, I.I. Syvorotka 1,2, M. Kushlyk 3,4, U. Yakhnevych 1, Ya. Zhydachevskyy 1,3, A.I. Popov5, O. Buryy 1, S. Kachan 1, A. Suchocki 3,6
1 Lviv Polytechnic National University, 12 Bandera st., Lviv, Ukraine.
2 Scientific Research Company “Electron-Carat”, 202 Stryjska st., Lviv, Ukraine
3 Institute of Physics PAS, 32/46 Al. Lotników, Warsaw, Poland
4 Ivan Franko National University of Lviv, 107 Tarnavskoho st., Lviv, Ukraine
5 Institute of Solid State Physics, University of Latvia, 8 Kengaraga st., Riga, Latvia
E-mail: popov@latnet.lv
6 Institute of Physics, University of Bydgoszcz, 11 Weyssenhoffa st., Bydgoszcz, Poland

GGG:Co2+ crystals are used for passive Q-switching in lasers operating at 1.3-1.5 µm [1]. It is known that presence of Ca2+ or Mg2+ ions leads to appearance in GGG of photochromic properties as well as agglomerations of point defects [2-4]. Co ions in GGG can be present both in the 2+ and 3+ oxidation states. Therefore photochromic properties can be also a feature of GGG:Co crystals and can effect on their functional properties. The work is devoted to studying of photochromic properties of GGG:Co (0.2 at.%). The attention was paid to registration of the absorption changes in GGG under exposure to laser radiation of 266, 325, 440 and 625 nm depending on the radiation power and the exposition dose. In as-grown CGG:Co the absorption bands related both to Co2+ and Co3+ ions can be revealed. Under laser exposure with λ = 325 nm, the crystal coloration is observed as a result of appearance of the bands at 282, 406 and 620 nm with clearness at 336 nm. An exposure of the crystal with λ of 440 or 625 nm leads to bleaching of the bands at 282, 406 and 620 nm. An exposure with λ = 266 nm has a dual effect depending on the irradiation time. The absorption changes observed under sequential illumination of the colored and cleared crystals with the mentioned λ allowed to assume that four different types of centers are involved these processes. Among them: a complex center, which includes Cо2+ ion and O vacancy as a compensator (absorption at 336 nm) [2, 4]; O- type center; F-center; and an isolated Co2+ ion (absorption at 620 nm). Basing on the mathematical modeling methods we attempt to evaluate energetic characteristics of the process of coloration at 336 and 406 nm.

1. Kravchenko V., Sadovskii P., Sobolev A. et al., Quant. Electron. 39 (2009) 1121. 
2. Matkovskii A., Vitruk L., Sugak D. et al., Opt. and Spectroscopy 67 (1989) 648. 
3. Ellaban M., Fally V., Rupp R.A., Kovacs L., Opt. Express 14 (2006) 593.
4. Matkovskii A., Potera P., Sugak D. et al., Cryst. Res. Technol. 39 (2004) 788.